The horseshoe crab, Limulus polyphemus, has been in existence for millions of years. Few sources of natural mortality exist. Predation by sea turtles, habitat degradation, spawning in sub-optimal habitats, algal infestation and gill ballooning are threats to the Limulus population. None of these, however, affects the population as seriously as human harvesting for use as bait.
Today, the horseshoe crab is an important multi-use resource that impacts the ecology and economy of the Atlantic Coast of the United States. In addition to having an established ecological role (e.g. in providing food for migratory birds), the horseshoe crab has also provided significant contributions to medicine. Chitin from the horseshoe crab's carapace can be used in dressing wounds of burn victims and in sutures. Additionally, a large body of research on the Limulus eye has provided insight to the functioning of the human eye. The most significant contribution of L. polyphemus to medicine, however, has been the discovery of Limulus amebocyte lysate (LAL). LAL is a clotting agent derived from the blood of the horseshoe crab that is now used as the sole test for endotoxins in medical equipment and intravenous drugs. Specifically, LAL coagulates in the presence of gram-negative bacterial endotoxins allowing for effective prevention and diagnosis of infections. LAL has revolutionized the medical industry by reducing the need for animal testing, thus making the practice of medicine safer and more efficient. Since the implementation of an FDA mandate requiring bacterial tests of all medical items for use in humans, LAL production has evolved into a million dollar industry.
In 1999, approximately 250,000 horseshoe crabs were captured and bled for LAL production. This number virtually doubled over 10 years from 130,000 in 1989, and the numbers continue to increase. Bled crabs are not destroyed. Instead they are required to be released after 72 hours of bleeding under FDA regulation. This regulation, however, may soon become optional as a proposed amendment to the Interstate Fishery Management Plan (FMP) would allow horseshoe crabs that are harvested for bait to be bled first and then used as bait. This amendment was passed in May 2004.
Horseshoe crabs have long been harvested as bait in the eel, conch, lobster and catfish fisheries. Specifically, the demand for horseshoe crabs now centers on the American eel and conch fisheries along the Atlantic coast of the US where horseshoe crabs are used to bait pots and traps. Eel are popular in that they are used primarily as bait by recreational fishermen throughout the US, as well as for human consumption, much of which involves exportation to Asia countries. There exists both a national and international market for conch meat as well. Eel and conch fishermen report that female horseshoe crabs are superior bait to fish, and result in superior catches that increase daily profits. Interestingly, female horseshoe crabs are considered superior bait to even male horseshoe crabs in the eel fishery, and, in fact this fishery generally uses only female horseshoe crabs as bait. As for conch fisheries, in 2000, a reported 97% of conch landings were caught with horseshoe crabs (Manion et al. 2000).
With the demand so high, it is estimated that 5000 female horseshoe crabs are used as bait per fisherman per year. In Delaware only 77 permits were issued for eel fishing in 2004, which translates to approximately 385,000 female horseshoe crabs removed from the reproductive population. Conch fisheries are estimated to remove 22,000 horseshoe crabs per fisherman per year. As large as these numbers are, they do not even include harvesting in other states (e.g. New Jersey issued 34 permits for Limulus harvesting in 2003).
The favored use of female horseshoe crabs places added pressure on the Limulus population. Once they reach maturity (approximately 9-12 years), female horseshoe crabs can lay as many as 80,000 eggs each year and typically spawn for many years. Under basic ecological principles, extraction of thousands of females from the population reduces the reproductive fitness of the population, thereby eliminating the potential for population growth.
Measures, at both the State and Federal levels, have been taken to minimize the loss in the horseshoe crab population. For instance, some states now require fishermen to purchase permits for legally harvesting horseshoe crabs and further require them to report their harvesting numbers each year. In addition, some states have placed restrictions on certain times of the day as well as certain days of the week when harvesting is allowed. Finally, some states require the use of bait bags. Even with these measures in place, however, problems continue to exist as enforcement is difficult and underreporting by permit holders occurs more often than not. Recently, Delaware attempted to institute emergency restrictions, but were met with considerable resistance by local fishermen who rely on horseshoe crabs to support their eel and conch catches, and, as such, their livelihood.
Therefore, there is a need for a long-term, sustainable alternative to the preferential use of horseshoe crabs as bait in the eel and conch fisheries. The development and implementation of an artificial bait in the eel and conch fisheries is one way to prevent decline of the horseshoe crab population. An effective artificial bait must be species-specific, cost effective, easy to store and transport, easy to prepare, able to withstand environmental changes and long periods of immersion, and functional at low concentrations of attractant. Additionally, a bait matrix must be resistant to penetration and destruction by microbes, thereby preserving the integrity of the attractant.
The inventors have determined the characteristics of an attractant found in horseshoe crab eggs and have used such characteristics to develop an artificial bait that does not rely on the natural source of the horseshoe crab egg attractant.